(1) Field of the Invention
The present invention relates to an integrated circuit with a trimming circuit in which one or more blown object fuses arbitrary determined among a number of fuses arranged in alignment are blown, and an apparatus and a method for producing the integrated circuit.
(2) Description of Related Art
In accordance with micromachining in process, a demand arises for reduction in chip area of an integrated circuit. For an integrated circuit with a trimming circuit in which one or more blown object fuses arbitrary determined among a number of fuses arranged in alignment are blown, reduction in area of such a trimming circuit is also desired.
However, when a fuse in such a trimming circuit is blown, blown fragments scatter from the blown fuse in some cases. There is possibility that a blown fragment reestablishes a short circuit on another blown fuse if the fuses are arranged at shorter intervals than the scattering distance of blown fragments.
FIG. 55 shows an example of arrangement of fuse blowing positions of fuses in a trimming circuit of a conventional integrated circuit with a relationship between a fuse blowing position and a blown fragment scattering area caused from the blowing of the fuse. In the example shown in FIG. 55, the distance between two adjacent fuses is smaller than a blown fragment scattering distance. The trimming circuit in FIG. 55 includes eight fuses (F1-F8) are arranged in parallel with one another at the same intervals and assumes that fuses F1, F3-F5, F7, and F8 are to be blown.
Since the distance between two adjacent fuses is smaller than a blown fragment scattering distance in FIG. 55, in sequentially blowing the blown fuses in order from fuse F1 to fuse F8, blown fragments generated by blowing fuse F4 may reach fuses F3 and F5 and may reestablish short circuits on the blown position of blown fuses F3 and F5. In the same manner, blown fragments generated by blowing fuses F5 and F8 may reach fuses F4 and F7 respectively and may reestablish short circuits on the blown position of these blown fuses F4 and F7 respectively.
FIG. 56 shows another example of arrangement of fuse blowing positions of fuses in a trimming circuit of a conventional integrated circuit with a relationship between a fuse blowing position and a blown fragment scattering area caused from the blowing of the fuse. In this example shown in FIG. 56, the blowing positions of contiguous fuses are different in a direction (the Y direction) orthogonal to the arrangement direction (the X direction) of the fuses. In also FIG. 56, eight fuses (F1-F8) are arranged in parallel with one another at the same intervals and fuses F1, F3-F5, F7, and F8 are to be blown.
In conventional laser trimming which blows a fuse with a leaser, the circuit size in the X direction has been reduced by varying (offsetting) the blowing position of contiguous fuses in the Y direction to widen the distance between the blowing position between the contiguous fuses.
For example, Patent Reference 1 listed below alternates a first blowing position in the Y direction orthogonal to the fuse arrangement direction X with a second blowing position different in the orthogonal direction Y so that the intervals for fuses is narrowed to reduce the size occupied by the arrangement of the fuses.
Further, below Patent Reference 2 discloses that in blowing two or more fuse electrodes connected to one another in the X direction and arranged in the Y direction by laser beams emitted from the Z direction, two contiguous fuse electrodes are blown at different position in the Y direction to avoid to reestablish short circuit on the continuous fuses. In other words, such blowing manner prevents scattering fragments generated by blowing a fuse electrode from reestablishing short circuits on contiguous fuse electrodes.
Patent Reference 3 discloses that, in a structure in which one or more fuses each having the width b are arranged in substantially parallel with one another at intervals a and each blown object fuse is blown by irradiating by laser beams which forms an irradiation area with radius d and which has a permissive error h for the irradiation position, interval a is determined such that interval a, width b, radius d, permissive error establishes a specific relationship in order to reduce the intervals of fuses and consequently reduces the arrangement area occupied by the fuses.
In another blowing method of electric trimming in which flow of electricity through a fuse generate a heat to blow the fuse, since it is difficult to control the blowing position in the orthogonal direction (the Y direction) to the direction (the X direction), fuses are arranged at wide intervals such that the distance between contiguous fuses comes to be larger than the scattering distance of blown fuse fragments. Namely, the following relationship is established:Scattering distance≦X-direction fuse interval
FIG. 57 is a flow diagram showing a succession of procedural steps of virtually blowing method (steps A10-A60) performed on a trimming circuit of a conventional integrated circuit.
In the conventional virtually blowing method, upon completion of setting a counter value (in a binary code) in fuses that are to be blown and that is same in quantity as the bits of the binary counter value (step A10), the fuses representing the counter value are virtually blown (step A20) and a control object section is measured (step A30). A determination is then made as to whether the counter value terminates (step A40). If the result of the determination is negative (NO route in step A40), the counter value is updated (step A50) and then the procedure returns to step A20. The counter value is updated by, for example, Regular falsi method or Bisection method.
Conversely, if the judgment result is positive (Yes route in step A40), the fuses are actually blown with the usable trimming value corresponding to the counter value (step A60).
[Patent Reference 1] Japanese Patent Application Laid-Open (KOKAI) No. HEI 6-120349
[Patent Reference 2] Japanese Patent Application Laid-Open (KOKAI) No. 2001-274251
[Patent Reference 3] Japanese Patent Application Laid-Open (KOKAI) No. 2001-57388
Although the progress in the process technique realizes makes process restriction to narrow the distance between fuses, fuses should be arranged such that direct distance between blowing positions of contiguous fuses is wider than scattering distance blown fragments generated by blowing a fuse so that the blown fuse fragments caused by blowing a fuse does not reestablish a short circuit on another blown fuse adjacent to the first fuse because two contiguous fuses may be determined to be blown object fuses, resulting in reestablishment of a short circuit. That cannot make the fuse interval narrow enough to reduce the area occupied by the trimming circuit.
FIG. 58 illustrates an example of arrangement of fuses in a trimming circuit of a conventional integrated circuit, and specifically shows the relationship between a blowing position of a fuse and the blown fragment scattering area caused from blowing the fuse. In an example of FIG. 58, the distance between every two contiguous fuses are set to be larger than the blown fragment scattering distance. In also FIG. 58, eight fuses (F1-F8) are arranged in parallel with one another at the same intervals and fuses F1, F3-F5, F7, and F8 are to be blown.
In a general trimming circuit, one or more blown object fuses are determined in terms of, for example, the chip properties, and therefore every fuse in the trimming circuit can be a blown object fuse. For this reason, a trimming circuit in a conventional integrated circuit sets the direct direction between the blowing positions of every two contiguous fuses to be larger than the blown fuse fragment scattering distance. Such a direct distance is realized by widening the distance between two blowing points in the fuse arrangement direction (the X direction) as shown in FIG. 58, or by widening the distance between two blowing points both in the fuse arrangement direction (the X direction) and in the orthogonal direction (the Y direction) to the arrangement direction. Consequently, the trimming circuit requires a large occupation area.
The manner in which the blowing positions of contiguous fuses are varied (offset) in a direction (the Y direction) orthogonal to the arrangement direction (the X direction) of the fuses surely shown in FIG. 56 can narrow the fuse interval in the X direction but needs to stretch the blowing positions in the Y direction, so that the fuse circuit results in an increased occupation area. In particular, the larger bits (the larger number of bits to be set) the larger occupation area caused from stretching in the Y direction.
Even in addition of offset in the Y direction, since scattering distance restricts the distance between blowing positions, the distance between contiguous fuses cannot be set narrower than about the half the scattering distance.
In addition, it is difficult for electric trimming to adjust blowing positions of fuses as explained above, the fuse interval in the X direction cannot be set narrower than the blown fragment scattering distance even if desires to.
With the foregoing problems in view, the object of the present invention to reduce the occupation area of the trimming circuit by efficiently arranging blowing positions on fuses.